1. Field of the Invention
The present invention relates to an illumination device and a manufacturing method therefor, a display device, and an electronic instrument and, in particular, to an illumination device that is advantageous when formed as a front light placed on the viewing side of a display device, and to a display device whose viewing side is provided with this illumination device, as well as to an electronic instrument provided with this display device.
2. Description of the Related Art
Conventionally, a reflective type of liquid crystal display device (electro-optical device) is known in which exterior light such as sunlight shines into the viewing side of a liquid crystal display panel, is reflected inside the liquid crystal display panel, and is then transmitted to the viewer""s side. However, because reflective type liquid crystal display devices are difficult to view in dark locations, a reflective type of liquid crystal display device provided with a front light (illumination device) on the viewer""s side of the liquid crystal display panel has been proposed.
Broadly speaking, a conventional front light is constructed from a light source disposed on one edge of the viewing side of the liquid crystal display panel, and a light guide plate that is disposed on the viewing side of the liquid crystal display panel and that guides light from the light source toward the liquid crystal display panel.
However, the problem when using the above conventional front light is that a part of the light emitted from the light source does not travel towards the liquid crystal display panel, but instead travel from the surface of the light guide plate on the viewer""s side directly towards the viewer (leakage light). As a result, the illumination efficiency is reduced and the leakage light causes the low contrast ratio of the liquid crystal display device leading to deterioration in the quality of the display.
The present invention was conceived in view of the above circumstances and it is an aim thereof to provide an illumination device that is capable of reducing the amount of light leaked that does not travel towards a display device but travels directly towards a viewer and that can thereby improve the illumination efficiency, and a manufacturing method for the illumination device, as well as a display device whose viewing side is provided with this illumination device, and an electronic instrument provided with this display device.
The illumination device of the present invention is provided with a transparent substrate having light emitting elements which are disposed on a surface thereof and which emit light, and the light emitting elements are provided with at least a transparent electrode, a light emitting layer, and a reflective electrode, in that order, from the outgoing surface of the transparent substrate.
That is, in the illumination device of the present invention, a reflective electrode functioning as a cathode electrode of the light emitting element reflects light emitted from the light emitting layer of a light emitting element, and then the reflected light travels towards a transparent electrode that functions as an anode electrode. As a result, light travels from one surface of a transparent substrate. Note that the illumination device of the present invention is provided on one side of the display device.
By employing a structure in which light that travels from the light emitting layer of a light emitting element is reflected by a reflective electrode and travels towards the opposite side of the reflective electrode in this way, when the illumination device of the present invention is provided in a display device, it is possible to reduce the amount of light leaked that does not travel towards the display device but travels from the illumination device directly towards the viewer. As a result, it is possible to obtain high contrast ratio. In addition, it is possible to illuminate efficiently towards the display device. As a result, the illumination efficiency is improved, and therefore power consumption can be reduced.
Furthermore, in the illumination device of the first aspect of the present invention, at least the reflective electrode of each light emitting element is formed in concavities that are formed having a pattern on one surface of the transparent substrate.
By forming at least the reflective electrode of each light emitting element inside the concavities that are formed on the transparent substrate, it is not necessary to perform a patterning process for at least the reflective electrodes of the light emitting elements. Accordingly, it is possible to simplify the patterning process.
It is also desirable that at least the reflective electrode and the light emitting layer of each light emitting element be formed in the concavities. By forming the light emitting layer inside the concavities in this way, the light emitting layer is wrapped with the transparent substrate, the reflective electrode, and the transparent electrode. Therefore, it is possible to prevent the light emitting layer from degradation. In particular, since the transparent substrate is made from a glass substrate or the like that has a low gas permeability, it is possible to prevent water vapor or the like from penetrating into the light emitting layer from the outside of the illumination device. Therefore, it is possible to prevent the light emitting layer from deteriorating.
Moreover, in the illumination device according to the first aspect of the present invention, it is desirable that the light emitting layer of the light emitting element consist of an organic electroluminescent material. Since the light emitting layer consists of an organic electroluminescent material that is capable of light emission at low voltages and that has a high level brightness, it is possible to reduce power consumption and to improve the illumination efficiency.
In the illumination device according to the first aspect of the present invention, it is also desirable that the concavities be formed on the outgoing surface of the transparent substrate; that the concavities have a concave curved bottom; and that at least the reflective electrode of each light emitting element be formed on the concave curved bottom of the concavities.
By forming concavities having a concave curved bottom on the outgoing surface of the transparent substrate and forming at least the reflective electrode of each light emitting element on the concave curved bottom of the concavities, it is possible to use the curved reflective electrode to condense the emitted light. Therefore, it is possible to reduce light leaking from the side of the light emitting elements and also to reduce the total reflected light within the transparent electrode and at the boundary between the transparent electrode and the light emitting layer. Accordingly, the light emitting element can emit light more efficiently, and the illumination efficiency can be improved.
It is also desirable that a protective layer be provided over the surface of the transparent substrate on which the concavities are formed so as to protect the light emitting elements.
The illumination device according to the first aspect of the present invention may be manufactured using a method in which, after the concavities have been formed on one surface of the transparent substrate with a pattern, at least the reflective electrode of the light emitting elements can be formed in the concavities.
Moreover, the illumination device may be manufactured using a method in which the concavities having a concave curved bottom are formed on one surface of the transparent substrate by isotropically etching after forming the resist in the pattern.
Furthermore, it is desirable that the light emitting elements have a layer structure which the transparent electrode, the light emitting layer, and the reflective electrode are sequentially formed in the concavities on the surface of the transparent substrate. Because the light emitting elements are formed by stacking the transparent electrode, the light emitting layer, and the reflective electrode in layers in sequence inside the concavities, it is possible to simplify the patterning process for the transparent electrode, the light emitting layer, and the reflective electrode.
By providing the illumination device according to the first aspect of the present invention in the viewing side of a display device, it is possible to reduce the amount of light leaked from the illumination device (that does not travel towards the display device but travels directly towards the viewer,) and to improve the illumination efficiency. Therefore it is possible to provide a display device such as an electro-optical device which consumes less power and shows higher contrast ratio and excellent display quality. Moreover, this display device makes it possible to provide an electronic instrument with excellent display quality and less power consumption.
Next, the present inventors discovered that when the planar structure of the light emitting elements has periodicity, if the illumination device is provided in a display device such as a liquid crystal display device or the like that is provided with pixels arranged in an array configuration, then the periodic structure of the light emitting elements interferes with the periodic structure of the pixels of the display device leading in some cases to moire stripes being generated. Therefore, the present inventors examined how to make the moirxc3xa9 stripes invisible.
For example, when the light emitting elements are formed in a lattice configuration, the period of the moirxc3xa9 stripes 1 is defined by the following Equation (1):                     l        =                                            d              1                        ⁢                          d              2                                                                          d                1                2                            +                              d                2                2                            -                              2                ⁢                                  d                  1                                ⁢                                  d                  2                                ⁢                cos                ⁢                                  xe2x80x83                                ⁢                θ                                                                        (        1        )            
Here, the angle between the direction in which the light emitting elements extend and the direction in which the pixels of the display device are aligned is xcex8, the interval between light emitting elements is d1, and the interval between the pixels of the display deice is d2.
As understood by Equation (1), when d1=d2 and xcex8=0, then the period 1 of the moirxc3xa9 stripes is at its longest and the moire phenomenon is most visible.
Accordingly, in the illumination device according to the second aspect of the present invention, when the pattern of the light emitting elements has periodicity, the present inventors discovered that if the interval of the light emitting elements (at least the interval of the reflective electrodes forming the light emitting elements) is different from the interval of the pixels of the display device, then it is possible to make the moirxc3xa9 stripes invisible even when the illumination device of the second aspect of the present invention is provided in a display device.
Note that when the pixels are arranged in an array configuration, two types of interval exist for the pixels of the display device. On the other hand, although one or a plurality of types of interval exist for the light emitting elements, in the illumination device of the second aspect of the present invention, it is desirable for all of the intervals of the light emitting elements and all of the intervals of the pixels of the display device to be different values.
In addition, the present inventors discovered that in the illumination device according to the second aspect of the present invention, when the light emitting elements are formed with a lattice pattern on one surface of the transparent substrate, and the direction in which the light emitting elements extend (at least the direction in which the reflective electrodes forming the light emitting elements extend) is not parallel to the direction in which the pixels of the display device, it is also possible to make the moirxc3xa9 stripes invisible.
Note that when the pixels are arranged in an array configuration, two types of alignment direction exist for the pixels of the display device. On the other hand, although one or extending directions exist for the light emitting elements, in the illumination device of the second aspect of the present invention, it is desirable that all of the extending directions of the light emitting elements be not parallel to all of the alignment directions of the pixels of the display device.
The present inventors also discovered that it is also desirable that, when the light emitting elements are formed with a lattice pattern on one surface of the transparent substrate, a structure be employed in which the intervals of the light emitting elements are different from the intervals of the pixels of the display device, and at the same time the extending directions of the light emitting elements are not parallel to the alignment directions of the pixels of the display device. The present inventors discovered that this structure makes it possible to make the moirxc3xa9 stripes invisible.
Furthermore, in the second aspect of the present invention, the present inventors also discovered that it is desirable for the intervals of the light emitting elements to be random on the surface of the transparent substrate, and that if this structure is employed, it is possible to make the moirxc3xa9 stripes invisible.
Examples of light emitting elements whose lattice pattern has periodicity are in a striped configuration, a square lattice configuration, and a hexagonal lattice configuration.
Moreover, in the illumination device according to the second aspect of the present invention, because the reflective electrode forming the light emitting elements is opaque, the light emitting elements are partially formed on the surface of the transparent substrate. Thus, the light emitting elements are aligned with some interval. The greater the interval between the light emitting elements, the more the illuminance on a display device decreases. However, the present inventors discovered that when the intervals between light emitting elements is less than 830 times the square of the distance between the light emitting element and the reflective layer of the display device, and when the illuminance just under the light emitting element is regarded as 100%, it is possible to obtain the illuminance of 50% or more on the surface of the display device, and therefore uniform illumination can be obtained when the second aspect of the present invention is provided in a display device.
Moreover, when the illumination device according to the second aspect of the present invention is provided in a display device, because the reflective electrode forming the light emitting elements is opaque, it is not possible to see the display where the light emitting elements are formed. Thus, if the area of the light emitting elements expands, the visibility of the display decreases when the illumination device according to the second aspect of the present invention is provided in a display device. Therefore, in the illumination device according to the second aspect of the present invention, it is desirable that the ratio of the area of the light emitting elements to the area of the transparent substrate be less than 0.5. By employing this setting, the display can be viewed when the illumination device of the second aspect of the present invention is provided in a display device.
Moreover, in the illumination device according to the second aspect of the present invention, it is desirable that the light emitting layer of the light emitting elements consist of organic electroluminescent material. By thus forming the light emitting layer such that it consists of an organic electroluminescent material, it is possible to emit light at low voltages with a high level brightness, and it is possible to reduce power consumption and to improve the illumination efficiency.
In addition, by providing the illumination device according to the second aspect of the present invention on the viewing side, it is possible to reduce the amount of light leaked from the illumination device that does not travel towards the display device but travels directly towards the viewer, and to improve the illumination efficiency, and to make the moirxc3xa9 stripes invisible. It is therefore possible to provide a display device with high contrast ratio and excellent display quality and less power consumption.
Furthermore, by installing this display device, it is possible to provide an electronic instrument that has excellent display quality and less power consumption.
Note that the light emitting elements according to each aspect of the present invention include at least one of organic electroluminescent elements, inorganic electroluminescent elements, and organic LEDs, and inorganic LEDs (light emitting diodes).